A fuel cell (cell), for example, a solid polymer electrolyte-type fuel cell, includes a layer of a membrane-electrode assembly (MEA) and a separator. The MEA includes an electrolyte membrane of an ion-exchange membrane, an electrode 14 (e.g., an anode, a fuel electrode) including a catalyst layer disposed on one side of the electrolyte membrane, and another electrode (e.g., a cathode, an air electrode) including a catalyst layer disposed on the other side of the electrolyte membrane. Diffusion layers may be disposed between the MEA and the separators, on the anode side and the cathode side, respectively. The MEA and the diffusion layers form a power generating reaction portion and are squeezed by an anode separator and a cathode side separator.
At a power generating region of the fuel cell, in the separators, a fuel gas passage for supplying fuel gas (e.g., hydrogen) to the anode and an oxidant gas passage for supplying oxidant gas (e.g., oxygen, usually, air) to the cathode are formed. At a surface of the separator, opposite the fuel gas passage and at a surface of the separator opposite the oxidant gas passage, a coolant passage for letting coolant (e.g., cooling water) flow is formed in the separators. At the power generating region of the fuel cell, the separators squeeze the MEA via the diffusion layers, whereby power is generated accompanied by production of water.
Conventionally, as disclosed in Japanese Patent Publication No. 2001-143725 and in FIGS. 12-15, when the reactant gas passages (the fuel gas passage 3 and the oxidant gas passage 4) are a serpentine passage (a passage having a turn portion in a serpentine manner), the separators 1 and 2 squeezing the power generating reaction portion 5 include a gas passage dividing rib 6 defining the serpentine passage and a lot of protrusions 7 formed in the passage. Further, when the reactant gas passages are a serpentine passage, although the reactant gas is consumed in the power generation, in order to ensure a gas speed higher than a predetermined speed, a passage width D2 at a downstream portion is adapted to be smaller than a passage width D1 at an upstream portion.
In the conventional separators, because an amount of consumed hydrogen and an amount of consumed oxygen in air differ from each other, and because gas passage division ratios by the gas passage dividing rib 6 of fuel gas side and oxidant gas side differ from each other, when the separators 1 and 2 squeeze the power generating reaction portion 5, the gas passage dividing rib 6 of the anode-side separator and the gas passage dividing rib 6 of the cathode-side separator do not coincide with each other. This occurs usually in a layering direction of the separator 1, the power generating reaction portion 5, and the separator 2. As a result, as illustrated in FIG. 14, at a region where the gas passage dividing rib 6 and the protrusion 7 squeeze the power generating reaction portion 5, a portion between adjacent protrusions 7 (a gas flow portion) cannot push the power generating reaction portion 5 against the gas passage dividing portion 6, whereby the power generating reaction portion 5 is deformed into a wavy shape to form a gas leakage passage 9 between the gas passage dividing rib 6 and the power generating reaction portion 5. As a result, as illustrated in FIG. 15, an amount of short-circuit gas flowing between gas passage portions located on opposite sides of the gas passage dividing portion 6 increases, whereby a problem that the power generating efficiency of the fuel cell lowers is caused.
If the gas dividing ribs 6 of the separators 1 and 2 were located so as to oppose each other in order to decrease the amount of gas passing under the gas passage dividing rib 6, the gas passage division ratio of the gas passage of at least one of the separators 1, 2 would be inappropriate. Thus, problems such as excessive or insufficient supply of reactant gas and insufficient blow-off of product water by gas flow, etc. may be newly caused.
Objects of the present invention include providing a fuel cell which can decrease an amount of gas passing under a gas passage dividing rib and maintaining a gas passage division ratio of a gas passage to a conventional ratio by increasing an area where separators contact a power generating reaction portion from opposite sides of the power generating reaction portion.